Ammonia recovery from municipal wastewater using hybrid NaOH closed-loop membrane contactor and ion exchange system

Abstract

Water scarcity is affected by population growth and increasing nutrients pollution. This study evaluated the integration of ion exchange-natural activated clinoptilolite zeolite (IEX-NZ) and hollow-fibre liquid–liquid membrane contactor (HF-LLMC) as an innovative and sustainable hybrid technology for ammonia recovery from treated urban wastewaters. The process is based on NaOH closed-loop process to i) ensure the extracted concentration of ammonia from the loaded zeolites and ii) enhance the transport of NH3 through the HF-LLMC. Regeneration of the IEX-NZ provided recoveries up to around 92% using 8% NaOH solution with concentration factors between 30 and 60 and a residual ammonium stream below 1 mg NH4+-N/L. Recovery of NH3 from NaOH solutions was carried out by HF-LLMCs using two different membrane chemistries: polypropylene (PP) and poly (4-methyl-1-pentene) (PMP) (>95%). A 1-D model was developed and used to describe the time evolution of NH3 concentration during the recovery process, to determine its mass transfer coefficient (9.5·107 m3/m2·s) and to quantify the undesired water co-transport (5.0·105 m3/m2·s). In addition, the model was used to analyse the influence of operational parameters on the membrane's permeability to maximise the concentration of the ammonium salts recovered as fertilisers. In this case, the 1-D algorithm was used to identify the needed stages to achieve residual levels of NH3 on the treated streams that promoted the NaOH closed-loop recycling to secure economic feasibility.